Hello from the W3C GRDDL Working Group,
HTML 4 introduced the profile attribute on the head element
a URI-based extension hook.
http://www.w3.org/TR/html4/struct/global.html#h-7.4.4.3
The use of this mechanism is not very common, but some
communities have endorsed it explicitly, for example:
<head profile="http://dublincore.org/documents/dcq-html/">
<title>Expressing Dublin Core in HTML/XHTML meta and link
elements</title>
in
Expressing Dublin Core in HTML/XHTML meta and link elements
DCMI Recommendation. 2003-11-30
http://dublincore.org/documents/dcq-html/
and
<head profile='http://gmpg.org/xmdp/samplehtmlprofile.html'>
in
Xhtml Meta Data Profiles (XMDP)
http://gmpg.org/xmdp/description
GRDDL is a mechanism for using XML documents, especially XHTML
documents, as Semantic Web data:
"This GRDDL specification introduces markup based on existing standards
for declaring that an XML document includes data compatible with the
Resource Description Framework (RDF) and for linking to algorithms
(typically represented in XSLT), for extracting this data from the
document."
-- http://www.w3.org/TR/grddl/
It lets source documents declare the syntax their written in using
pointers to convert this syntax to the standard RDF/XML syntax. The
pointers can be either direct or indirect, via a namespace document
or HTML profile.
At least a few web sites are using GRDDL to formalize microformats data
as Semantic Web data:
http://2007.xtech.org/public/schedule/detail/15http://www.semantic-conference.com/2007/sessions/r3.html
and there are several interoperable implementations and
a reasonably complete test suite of GRDDL:
http://esw.w3.org/topic/GrddlImplementationshttp://www.w3.org/2001/sw/grddl-wg/td/test_results
The GRDDL use cases document discusses scenarios where consumers
use tools like HTML tidy to use HTML documents as if they were
XML.
http://www.w3.org/TR/grddl-scenarios/#html_tidy_use_case
While the current scope of GRDDL is limited to XML and XHTML,
it is mostly specified in terms of XPath, and it seems likely
that HTML 5 should work with XPath much the way XHTML does,
so that an HTML 5 parser should take the place of
HTML tidy plus an XML parser. So it looks technically straightforward
to revise GRDDL to work with HTML 5. Several of the implementations
already anticipate such a revision and support HTML documents
that are not well-formed XML by way of a "tag soup" parser.
The profile attribute on head is noted as one of the
attributes absent from current HTML 5 drafts.
http://www.w3.org/html/wg/html5/diff/#absent-attributes
We suggest adding it. The specification text in HTML 4 is
adequate in our experience.
http://www.w3.org/TR/html4/struct/global.html#h-7.4.4.3
If HTML 5 doesn't preserve this hook from HTML 4
and XHTML 1, the use of head/@profile will be less
formally ratified, but it seems unlikely to change.
Since implementations already exploit, it
seems likely that authors will continue to use it.
The cost of (re-)standardizing this markup seems moderate
and less than the value of preserving the current investment
in head/@profile into HTML 5 combined with the benefit
of endorsing this connection between HTML 5 and the
Semantic Web via GRDDL.
Dan Connolly and Harry Halpin for the W3C GRDDL Working Group
http://www.w3.org/2001/sw/grddl-wg/